This invention relates to a method of, and an apparatus for, making a formed wire, for example, a formed wire constituting a spring structure for a seat, bed or the like from a wire rod.
A formed wire is shown by way of example in FIG. 1. According to the conventional method, a linear wire is bent into a form spread in a plane as shown in FIG. 2; and then, portions A and B, which are called torque bars, are formed by twisting as shown in FIG. 3, whereby a formed wire having a three-dimensional shape as shown in FIG. 1 is obtained. This twisting is called "fish-mouth forming" in view of the shape of the product and it is common in the field of wire forming.
The method of making a formed wire by two steps, i.e., planar bending and fish-mouth forming, as hereinabove described, has a number of drawbacks as will hereinafter be pointed out.
Firstly, the method requires two separate machines, i.e., a planar bending machine and a fish-mouth forming machine. This leads to a high cost of facilities with necessity for correspondingly large manpower for operation. For automatic operation, a transportation apparatus, a loading apparatus and the like are required for connecting the two steps. Secondly, it is difficult to ensure accuracy in the shape of the product. Although the possibility of the springing back of the wire and the change in the shape of the formed wire due to heat treatment are taken into consideration in forming operations, there occurs a large fluctuation in the accuracy of the shape, since forming by twisting permits a high degree of elastic recovery as compared with forming by bending only.